The invention relates to a code reader having an integrated light source for the illumination of a reading zone and having a sensor matrix and an optical receiving system positioned in front of said sensor matrix.
Code readers are known in a variety of embodiments from the prior art and are also used inter alia to read codes which were applied directly to the respective carrier material by a deformation thereof. Codes of this type, which are known, for example, as so-called DPM codes (direct part marking codes), are generated, for example, in that the carrier material is acted on by a high-energy laser or by means of pin stamping (“dot peening”). It is common to both methods that recesses or indentations are generated in the carrier material at the respective desired positions which then ultimately correspond to the desired code in their total arrangement.
DPM codes are in particular used for two-dimensional codes which consist, for example, of dots directly arranged inside an area, with each dot corresponding to a recess or indentation in the carrier material.
The reading of DPM codes is difficult when the code reader is arranged perpendicular above the code, since the light source integrated in the code reader then illuminates the code at an angle of incidence which coincides at least largely with the optical axis of the code reader, which has the consequence that no great contrast difference occurs between the regions of the carrier material provided with recesses and those regions which do not have any recesses. Accordingly, one usually does not work with a light source integrated in the code reader here, but rather with an external light source which has to be provided separately and which illuminates the code at a very oblique angle of incidence in the sense of dark field illumination. Those regions of the carrier material having no recesses in this case generate a very flat light reflection so that the reflected light does not reach the code reader and the said regions in the code reader ultimately appear dark. The light obliquely incident onto the recesses is, in contrast, reflected to the code reader to a sufficient degree with an oblique light incidence such that the recesses ultimately appear light in the code reader and can be clearly distinguished from those regions—which appear dark—which have no recesses.
The fact is thus disadvantageous in the described known arrangements for the reading of DPM codes that the integrated light source usually present in a code reader cannot be used and an external light source additionally has to be provided which provides the described oblique illumination of the code. This external light source must furthermore be correctly adjusted relative to the code reader which signifies an additional effort.